Recording apparatus with improved S/N ratio

ABSTRACT

An information signal recording apparatus for recording an information signal having a predetermined frequency band onto a recording medium, which comprises signal separating means for receiving said information signal and for separating the received information signal into a first signal having a first frequency band and a second signal having a second frequency band which is higher than said first frequency band and outputting said first and second signals; first recording means for forming a frequency-modulated first signal by frequency-modulating the first signal outputted from said signal separating means and for recording said frequency-modulated first signal onto a first area of said recording medium; and second recording means for forming a frequency-modulated second signal, which is interleaved relatively to said frequency-modulated first signal, by frequency-modulating the second signal outputted from said signal separating means and for recording said frequency-modulated second signal onto a second area of said recording medium which is different from said first area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an information signal recording apparatus forrecording an information signal having a wide frequency band onto arecording medium.

DESCRIPTION OF THE RELATED ART

The luminance signal component of a TV signal has been prescribed tohave a frequency band of about 4.2 MHz. Meanwhile, as a result ofdecrease in cost of semiconductor memories, it has recently come to bepracticed to minimize a flicker and to increase vertical resolution byconverting scanning lines in such a way as to change an interlacedpicture plane into a non-interlaced picture plane.

However, although the vertical resolution can be increased by this,there arises an unbalanced state between the horizontal and verticalresolutions, because the band of 4.2 MHz which defines the horizontalresolution has not been determined relative to the vertical resolutionobtained in the case of interlacing arrangement.

To eliminate this unbalance, efforts have become active to raise thefrequency band up to 6 MHz or thereabout. These effects include, forexample, a movement for EDTV (extended definition television). In thecase of EDTV, in order to retain interchangeability with the signals tobe handled by the conventional transmission method, a transmissionsystem is arranged, for example, to separate only a high frequencycomponent which has frequencies, for example, from 4 to 6 MHz and tofrequency interleave and multiplex transmit the component thusseparated.

It is also being contemplated for a still picture recording/reproducingsystem, such as a still video system which requires a high degree ofdefinition in particular, to record a high frequency component and a lowfrequency component separately on a recording medium.

FIG. 5 of the accompanying drawings is a circuit diagram showing thereproduction system of the above stated still video system. As shown,the conventional system has been arranged in to reproduce the generallow frequency component and the high frequency component separately fromeach other and then to add them together before various signalprocessing operations.

The arrangement of FIG. 5 simplifies the circuit arrangement as itrequires only a single signal processing circuit 22. On the other hand,however, the conventional system is disadvantageous for removing noises.According to this arrangement, the noise removal must be carried out byfirstly removing the noise in the high frequency component and thenremoving the noise in the combined signal including the high frequencycomponent and the low frequency component. Therefore, the conventionalsystem either has complicated the signal processing operation or greatlydegraded the resolution of the picture.

The still video systems have unified standards already established forthem. In accordance with the standards, a still video system is allowedto record and reproduce a luminance signal of a frequency band up to 4.5MHz. However, this value 4.5 MHz (more exactly stated, 4.2 MHz in thecase of the NTSC color system) has been determined by the NTSC on theassumption of recording and reproduction of a motion picture. Hence,this value is not apposite to recording and reproduction of a stillpicture.

Further, as mentioned in the foregoing, the non-interlacing arrangementfor TV receiver which has been prompted by the recent improvement in theperformance of semiconductor memories has come to result in an increasein the vertical resolution which now presents a problem with respect tothe unbalance of the horizontal resolution relative to the increasedvertical resolution.

SUMMARY OF THE INVENTION

It is therefore an object of this invention to provide an informationsignal recording apparatus which is arranged to improve the S/N ratio ofan information signal.

It is another object of this invention to provide a recording apparatuswhich is arranged not only to eliminate the shortcoming of the abovestated conventional apparatus but also to have interchangeability, forexample, with the existing still video systems.

To attain this object, an embodiment of this invention comprises

(A) signal separating means for receiving an information signal and forseparating the received information signal into a first signal having afirst frequency band and a second signal having a second frequency bandwhich is higher than said first frequency band and outputting said firstand second signals;

(B) first recording means having a first magnetic head to record thefirst signal outputted from said signal separating means onto a firstarea of said magnetic recording medium by said first magnetic head; and

(C) second recording means having a second magnetic head, which isdifferent in its azimuth angle of gap from said first magnetic head, torecord the second signal outputted from said signal separating meansonto a second area of said magnetic recording medium, which is differentfrom said first area.

According to this embodiment, it is possible to record a signal of afirst frequency band of the information signal onto a first area of therecording medium and to record a signal of a second frequency band ofsaid information signal onto a second area of the recording medium,without causing cross-talk.

Another embodiment of this invention comprises:

(A) signal separating means for receiving an information signal and forseparating the received information signal into a first signal having afirst frequency band and a second signal having a second frequency bandwhich is higher than said first frequency band and outputting said firstand second signals;

(B) first recording means for forming a frequency-modulated first signalby frequency-modulating the first signal outputted from said signalseparating means and for recording said frequency-modulated first signalonto a first area of said recording medium; and

(C) second recording means for forming a frequency-modulated secondsignal, which is interleaved relatively to said frequency-modulatedfirst signal, by frequency-modulating the second signal outputted fromsaid signal separating means and for recording said frequency-modulatedsecond signal onto a second area of said recording medium which isdifferent from said first area.

According to this invention, it is possible to frequency-modulate asignal of a first frequency band of the information signal and recordthe frequency-modulated signal onto a first area of a recording mediumand to frequency-modulate a signal of a second frequency band of saidinformation signal into a signal which is interleaved with saidfrequency-modulated signal of the first frequency band to record thefrequency-modulated signal onto a second area of said recording medium,thereby avoiding occurrence of mutual adverse affects owing tocross-talk between the signals recorded on said first area and on saidsecond area.

The above and further objects and features of the invention will becomeapparent from the following detailed description of embodiments thereoftaken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing the arrangement of a still videosignal reproducing apparatus arranged according to this invention as afirst embodiment thereof.

FIG. 2 is a block diagram showing the details of a noise limiterincluded in FIG. 1.

FIG. 3 shows a manner in which signals are recorded on a video floppydisc.

FIG. 4 shows the frequency band of a luminance signal to be handled bythe first embodiment.

FIG. 5 is a diagram showing the arrangement of the conventionalapparatus.

FIG. 6 is a block diagram showing the recording system of a magneticrecording/reproducing apparatus arranged according to this invention asa second embodiment thereof.

FIG. 7 is a block diagram showing the reproducing system of the secondembodiment.

FIG. 8 shows an example of a division of a frequency band of a videosignal.

FIG. 9 illustrates a state where a head is located at a most deviatedposition relative to a track on a magnetic disc.

FIG. 10 shows the arrangement of a head part.

FIG. 11 shows a frequency allocation where a high frequency componenthas been frequency-modulated.

FIG. 12 illustrates a relation between a deviation of a head relative toa track on a magnetic disc and an amount of cross-talk produced when anazimuth angle of a gap of a head φ=30°.

FIG. 13 illustrates a relation between an azimuth angle of a gap of ahead φ and a minimum C/N value.

FIG. 14 is a block diagram showing the recording system of a magneticrecording/reproducing apparatus arranged as a third embodiment of theinvention.

FIG. 15 is a block diagram showing the reproducing system of the sameembodiment.

FIG. 16 is a block diagram showing the recording system of a magneticrecording/reproducing apparatus arranged according to the invention as afourth embodiment thereof.

FIG. 17 is a block diagram showing the reproducing system of the sameembodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This invention will be more fully understood through the followingdetailed description of preferred embodiment thereof: FIG. 1 shows thewhole arrangement of a video signal reproducing apparatus embodying thisinvention as a first embodiment thereof. The illustration includes avideo floppy disc 401; a reproducing head 402; a reproducing head 403;step-up transformers 404 and 405; pre-amplifiers 406 and 407; frequencydemodulators 408 and 409; a deemphasis circuit 410; a frequencyconverter 411 which is arranged to perform conversion to a highfrequency band; a local oscillator 412; a low-pass filter (LPF) 413; adeemphasis circuit 414; a band-pass filter (BPF) 415; clamp circuits 416and 417; first and second noise limiters 418 and 419 which are arrangedto have different noise removing characteristics; an adder 420; and asignal processing circuit 421.

FIG. 2 shows in a block diagram the details of the noise limiter 418 or419. The limiter includes a variable gain amplifier 51; a noise removingcircuit 52 which is arranged to cut off a signal component below a noiseremoving level; and a noise removal level setting circuit 53 which isarranged to set the above stated noise removing level. Both the noiselimiters 418 and 419 of FIG. 1 are arranged as shown in FIG. 2. However,they differ in the setting value of the noise removing level.

The video floppy disc 401 is arranged to have high frequency componentand low frequency component recorded thereon with the high frequencycomponent azimuth recorded within a guard band part thereof separatelyfrom the low frequency component. More specifically, with the frequency4 MHz of a luminance signal set as a boundary, a luminance signalcomponent below 4 MHz (or low frequency component) and a color signalare recorded in the same manner as in the ordinary still video recordingsystem on one hand. On the other, a luminance signal component withinthe range from 4 to 6 MHz (or high frequency component) is first lowfrequency hand converted by means of a suitable locally oscillatedfrequency and then is frequency modulated after a suitable emphasizingprocess. After these processes, the high frequency component is azimuthrecorded within the guard band part as shown in FIG. 3.

The noise limiters 418 and 419 which are carrying out an essentialfunction according to this invention are further described as follows:Each of the noise limiters removes a signal below a certain level byregarding it as a noise. However, the amplitude level of the signalgenerally decreases according as the frequency of the signal increases.Therefore, if the noise removing level is set at a high level, the noiselimiter would remove even a high frequency component of the signal. Inthat event, the noise removal would result in an image havinginsufficient sharpness. Since the noise of high frequency is notconspicuous, it is rather preferable to have the noises of a highfrequency region not completely removed. In the light of this, while thefirst noise limiter 418 which is provided for the low frequencycomponent is arranged to have the noise removing level set at arelatively high level, the second noise limiter 419 which is for thehigh frequency component is arranged to have the noise removing levelset either at a low level or even at a zero level. With the noiselimiters arranged in this manner, the S/N ratio of the signal as a wholeis greatly improved by removing the conspicuous noises in theintermediate frequency region of the signal while the noises in the highfrequency region thereof is not much removed or not removed at all, sothat an image of a high definition can be obtained.

As apparent from comparison between the embodiment of the inventionshown in FIG. 1 and the example of the conventional apparatus shown inFIG. 5, the above stated advantage is attainable by the mere addition ofanother noise limiter. The embodiment, therefore, incurs little increasein the cost of manufacture.

Further, in cases where the low frequency component and the highfrequency component have been subjected to pre-emphasizing processes ofthe same characteristic, the noise removing and adding (combining)processes may be carried out before a deemphasizing process. Further,even in case that the pre-emphasizing process of the same characteristicis not performed on the low frequency component and the high frequencycomponent, the noise limiters may be still disposed before a deemphasiscircuit.

The variable gain amplifier 51 which is included in each of the noiselimiters permits adjustment to a suitable value of a ratio in whichluminance signal components YS and YH are added together by changing thegain of the amplifier 51 (see FIG. 4).

In the foregoing, the embodiment is described with reference to FIGS. 1to 4 as being arranged to perform field recording. However, theembodiment can be arranged in exactly the same manner also for framerecording.

While the embodiment has been described as being arranged to reproduceimage information signal recorded on the magnetic recording medium, thisinvention is of course likewise applicable to a case where a videosignal is to be transmitted. Further, while the invention has beendescribed as applied to a still video system, the signal processingoperation can be likewise carried out also for moving pictures inaccordance with the invention.

Since the first embodiment of this invention is arranged to perform thenoise removing process on the low frequency component and the highfrequency component separately from each other, the embodiment iscapable of improving the S/N ratio and giving a picture of a high degreeof definition.

A second embodiment of this invention is arranged as follows: The secondembodiment is fundamentally arranged to have a luminance signal which isof a frequency band up to 6 MHz into two at about 4 MHz and to have highfrequency component (luminance signal) of a band from 4 to 6 MHz azimuthrecorded in a guard band part of a disc-shaped recording medium (i.e. amagnetic disc). FIG. 8 illustrates an example of division of a frequencyband of the luminance signal. The high frequency component. YH isrecorded in the guard band part of the magnetic disc by frequencyconverting and frequency modulating it. In this instance, it isnecessary to take head to the following points for interchangeabilitywith the conventional still video system: (1) cross-talk betweenadjacent tracks and (2) the S/N ratio of the high frequency componentsignal. These two points must be arranged to be compensable within therange of mechanical precision of the conventional or existing stillvideo system. The condition for meeting this requirement is as follows:

In accordance with the standard specifications currently prevalent, themaximum degree of track deviation is ±14 μm. Referring to FIG. 9, inazimuth recording the high frequency component in the guard band part ofthe magnetic disc, the position of the head deviates farthest on oneside in the worst case. In reproduction, the head position deviatesfarthest on the other side. Therefore, as indicated by a part d in FIG.9, the overlapped part of the azimuth recording within the guard bandpart is 12 μm.

In the actual preparation of a head having an azimuth angle of a Readgap, it is necessary to have some parts Δ on both sides of the head gapas shown in FIG. 10. Assuming that the part Δ measures about several μmto 8 μm, the distance of the above stated overlapped part d becomes 4 to10 μm. In other words, the azimuth recording width, that is, the widthof a recordable part in the direction perpendicular to the guard bandpart is -8×2 (max. Δ×2)=24 μm to 40 μm.

Under the above stated condition, the frequency allocation for frequencymodulation and the azimuth angle range necessary in obtaining the S/Nratio required for the high frequency component YH are obtained asfollows:

To better the conditions necessary against carrier cross-talk, thefrequency allocation is preferably made as high as possible and thelower side band is arranged to be not too wide in such a way as toobtain a low carrier frequency. In other words, since the band of thehigh frequency component signal is 2 MHz, the frequency deviation ispreferably held below 1 MHz. Therefore, the frequency allocation for thefrequency modulation becomes as shown in FIG. 11. The S/N ratio obtainedin this instance is computed in accordance with the following formula,which permits C/N-to-S/N conversion in close proximity: ##EQU1## In casethat the width of the main head which is arranged to record the videosignal of 0 to 4 MHz is 60 μm, the C/N of 10 KHz at the innermostperipheral part is 55 dB. Then, in the case of a head having an azimuthangle of a head gap the overlapping width of the signal track and thehead gap becomes 4 μm in the worst case and, with the azimuth angleassumed to be φ, the output level of the head decreases by 20 log₁₀ cosφ. As for the allowable limit of the S/N ratio, since the signal to behandled is within a high frequency band where random noises are notconspicuous, the allowable value is set at 40 dB without weighting.Further, the value K is arranged to be 10 dB by means of the noiselimiter, etc. and through a degree of emphasis. This arrangement gives avalue of φ≲60°. This value is in close proximity to the results ofexperiments.

The arrangement of the embodiment with respect to cross-talk betweenadjacent recording tracks is as follows: If any improvement in terms ofvisual sensation is not made by using carrier signals havinginterleaving relation with each other, as the carrier signals foreffecting the FM modulation, the allowable limit to the carriercross-talk between non-correlated signals is generally considered to be30 to 34 dB. If carrier signals having interleaving relation with eachother are used as the carrier signals for effecting the FM modulation, areducing effect is obtained by about 10 dB in terms of visualsensations. In that event, the allowable limit to the cross-talk betweenadjacent tracks is 20 to 24 dB ("National Technical Report, 1975, 4-HrVHS-VTR"). With the angle of the azimuth head gap assumed to be φ, theamount of cross-talk occurring during azimuth recording is obtained fromthe following formula: ##EQU2## wherein C: carrier signal

W: track width

φ: azimuth angle

N: cross-talk carrier signal

ΔW: track deviation amount

λ: wave length of recording signal.

In the above formula, the track width W is assumed to be 60 μm; and themaximum amount of track deviation ΔW to be 14 μm. As for the wave lengthof recording signal λ, with the maximum frequency 6.5 MHz assumed to beλmax when the outermost circumference γ of the magnetic disc is 20 mm,the wave length of recording signal λ can be expressed as follows:##EQU3##

FIG. 12 shows a relation between C/N (the amount of cross-talk in thiscase) and the amount of track deviation ΔW which is obtained when theazimuth angle φ is 30 degrees. FIG. 13 shows the azimuth angle φ inrelation to the minimum value of C/N.

As apparent from the above, it is 10°≦φ from the point of cross-talk.This well coincides with the results of experiments. It is thereforeapparent that the azimuth angle should be: 10°≦φ<60°. With the azimuthangle thus determined, the required accuracy of the azimuth angle mustbe obtained with regard to an azimuth loss L from the following formula:##EQU4##

The result of computation according to the above formula shows that theallowable error range of the azimuth angle is about 0.3 degree.

FIG. 6 shows in a block diagram the recording system of the magneticrecording/reproducing apparatus arranged as the second embodiment of theinvention. The luminance signal which is of a frequency band up to 6 MHzis supplied to a frequency separation circuit 601 to be frequencydivided at the frequency of 4 MHz as shown in FIG. 8. In actuality, thecircuit 601 is arranged to frequency divide the input signal by means ofan LPF and a BPF. Then, the high frequency component signal of afrequency band from 4 to 6 MHz thus obtained by frequency division issupplied to a frequency conversion circuit 602 to be converted into asignal of a low frequency band from 0 to 2 MHz or thereabout by using asignal of 3.58 MHz, etc. produced from a local oscillation circuit 603.Although it is omitted in FIG. 6, there is naturally provided an LPF forthe purpose of shaping.

The signal produced from the frequency conversion circuit 602 issupplied to an emphasis circuit 604 to be subjected to a suitableemphasizing process, which is preferably arranged to give dynamicemphasis. The output of the circuit 604 is frequency modulated by afrequency modulation circuit 605. The output of the circuit 605 iscurrent amplified by a recording amplifier 606. An amplified signal thusobtained is supplied via a step-up transformer 607 to a sub head 608.The head 608 then azimuth records the signal on a recording mediumwithin a guard band part thereof.

Meanwhile, the signal of frequency band from 0 to 4 MHz obtained by thefrequency separating circuit 601 and chrominance signals(color-difference signals) are frequency multiplexed through the samecircuit arrangement as that of the conventional still video systembefore they are recorded by a main head 615 on the recording medium.More specifically, the signal of the frequencies 0 to 4 MHz from thefrequency separating circuit 601 is supplied to an emphasis circuit 610to undergo an emphasizing process. The output of the circuit 610 isfrequency modulated by a frequency modulation circuit 611. The output ofthe circuit 611 is supplied to one of the input terminals of an adder612. Further, the color difference signals are converted into a colordifference line sequential signal by a color difference line sequencecircuit 620. The output of the circuit 620 is subjected to anemphasizing process at an emphasis circuit 621. The output of thecircuit 621 is supplied to a frequency modulation circuit 622. In thisinstance, if the color difference line sequential signal thus receivedis frequency modulated as it is, beating would be caused by aliasingnoises. To avoid this, the frequency band modulation is performed at ahigh frequency. The signal thus frequency modulated is supplied via aBPF 623 to a frequency conversion circuit 624. The circuit 624 thenconverts this signal to a low frequency band by using a signal which isproduced from a local oscillation circuit 625 and is, for example, at afrequency of 3.58 MHz. The output of the frequency conversion circuit624 is supplied to the other input terminal of the adder 612. The adder612 then frequency multiplexes the two input signals. The output of theadder 612 is current amplified by a recording amplifier 613. The outputof the amplifier 613 is supplied via a step-up transformer 614 to themain head 615.

FIG. 7 shows in a block diagram the reproduction system of the magneticrecording/reproducing apparatus arranged as the second embodiment. A subhead 701 is arranged to detect a signal which is recorded in the guardband part of a recording medium (i.e. the high definition informationcomponent which is within a frequency band from 4 to 6 MHz and isincluded in a video signal). The signal which is thus taken out from thesub head 701 is supplied via a step-up transformer 702 to a preamplifier703. After that, the signal has its wave form equalized by a wave formequalizing circuit 704. The output of the circuit 704 is frequencydemodulated by a frequency demodulation circuit 705. The output of thecircuit 705 is deemphasized by a deemphasis circuit 706. The output ofthe circuit 706 is supplied to a frequency conversion circuit 707 tohave the frequency thereof raised through a beat-up process as much asthe frequency value lowered by the recording system by using a signalproduced from a local oscillation circuit 708. The output of the circuit707 is supplied via a BPF 709 to one of the input terminals of an adder718.

A main head 710 is arranged to detect a video signal (i.e. the signalcomponent from 0 to 4 MHz) recorded on the recording medium. The signalfrom the main head 710 is processed by a step-up transformer 711 and apre-amplifier 712. The output of the pre-amplifier 712 is divided into aluminance signal and a chrominance signal by means of a BPF 713 and anLPF 720. The luminance signal which is produced from the BPF 713 isprocessed by an ordinary demodulating system including a wave formequalizing circuit 714, a frequency demodulation circuit 715, adeemphasis circuit 716 and an LPF 717 to be thus made into a luminancesignal of frequencies up to 4 MHz or thereabout. The luminance signal isthen supplied to the other input terminal of the adder 718. The adder718 then adds together the two inputs which are the signal offrequencies up to 4 MHz and the high frequency component signal offrequencies from 4 to 6 MHz. The adder thus produces a luminance signalof the original frequency band of 6 MHz which was obtained at the timeof recordeding on the recording medium.

The chrominance signal which is produced from an LPF 720 is supplied toa wave form equalizing circuit 721 to have its wave form equalized. Toprevent occurrence of moire due to aliasing noises produced at ademodulating part, a frequency conversion circuit 722 is arranged toraise the frequency of the output of the wave form equalizing circuit721 by using a signal of a frequency of 3.58 MHz or thereabout producedfrom a local oscillation circuit 723. After this, the chrominance signalis frequency demodulated by a frequency demodulation circuit 724. Theoutput of the demodulation circuit 724 is supplied via an LPF 725 to acolor difference concurrence circuit 726 to be subjected to aninterpolating process. The circuit 726 thus converts this input signalinto concurrent color difference signals. The reproducing system thusproduces the color difference signal along with the luminance signal of6 MHz.

This invention is not limited to a still video system but is alsoapplicable to any other system having a guard band on the recordingmedium. While the second embodiment is fundamentally arranged to becapable of recording high frequency component as described in theforegoing if there is high frequency component, the embodiment iscompatible with a system of the kind having no high frequency component.

Furthermore, in the case where at the time of recording the video signalis FM-modulated and then recorded, while at the time of reproduction thesignal is reproduced from the recording medium and then FM-demodulatedand where the carrier signals having interleaving relation with eachother are used as the carrier signals for effecting the FM-modulationand the FM-demodulation, the second embodiment operates as follows:

The process in which the carrier signals having interleaving relationwith each other are used as the carrier signals for effecting theFM-modulation of the video signal is employed for the purpose ofbringing cross-talks into a line offset relation. By this, cross-talkscan be mitigated in terms of visual sensation. Generally, this processcan be carried out by arranging the following relation to obtain betweenthe carrier fc(m) of an m-th field and the carrier fc(m+1) of an m+1-thfield: ##EQU5## (wherein n: an integer and fH: horizontal scanningfrequency)

In another method of carrying out this process, the phase of the carrieris inverted for every filed (the line offset state is obtainable byinterleave scanning). The term "cross-talks" means an azimuth signal inrelation to a main track signal and the main signal in relation to theazimuth signal.

FIG. 14 shows in a block diagram the recording system of a magneticrecording/reproducing apparatus which is arranged as a third embodimentof this invention. In FIG. 14, the parts which are the same as those ofFIGS. 1 to 13 are indicated by the same reference numerals. A luminancesignal of frequencies up to 6 MHz is supplied to a frequency separatingcircuit 601 which frequency divides it into two at a frequency of 4 MHzas shown in FIG. 8. In actuality, the circuit 601 performs thisfrequency division by means of an LPF and a BPF. A high frequencycomponent signal which is thus separated and is within a frequency bandfrom 4 to 6 MHz is frequency converted to a signal of frequenciesbetween 0 to 2 MHz by a frequency conversion circuit 602 which uses asignal produced by a local oscillation circuit 603 at a frequency of,for example, 3.58 MHz. Although it is not shown in FIG. 14, an LPF isprovided for the purpose of shaping in this instance. The signal thusobtained from the frequency conversion circuit 602 is supplied to anemphasis circuit 604. The circuit 604 performs a suitable emphasizingprocess (preferably dynamic emphasis) on the signal. The output of theemphasis circuit 604 is supplied to an interleaving DC voltage fieldoffset circuit 632. The circuit 632 then gives a DC potential differencefor every field as much as a value Δυ which can be expressed as follows:

    Δυ×β=fH/2

(wherein β represents the control sensitivity of a frequency modulator.)

The reason for such an offset: For accurate recording or reproduction,the signal must be decided to be for an odd-number or even-number field.A discrimination is thus made between an odd-number field and aneven-number field by means of a signal from an even- or odd-number fielddiscriminating signal generator 631.

The signal which is thus processed by the interleaving DC voltage filedoffset circuit 632 is supplied to a frequency modulation circuit 605 tobe frequency modulated there. The output of the circuit 605 is currentamplified by a recording amplifier 606. The amplified signal is suppliedvia a step-up transformer 607 to a sub head 608. The head 608 azimuthrecords the signal within a guard band part of a recording medium.

In the meantime, another signal of frequencies from 0 to 4 MHz which isseparated by the frequency separation circuit 601 and chrominancesignals (or color difference signals) are frequency multiplexed byexactly the same circuit arrangement as the conventional still videosystem. The multiplexed signals are then recorded on the recordingmedium by a main head 615.

More specifically, the signal of frequencies 0 to 4 MHz from thefrequency separation circuit 601 is subjected to an emphasis processcarried out by an emphasis circuit 610. The signal is then supplied toan interleaving DC voltage field offset circuit 633. Then, like theabove stated offset circuit 632, the circuit 633 gives a DC potentialdifference to the signal for every field on the basis of a signalgenerated by the even- or odd-number filed discrimination signalgenerator 631. The signal which is thus processed by the circuit 633 isfrequency modulated by a frequency modulation circuit 611. The frequencymodulated signal is then supplied to one of two input terminals of anadder 612. Meanwhile, the color difference signals are supplied to acolor difference line sequence circuit 620 to become a color differenceline sequential signal on the basis of a signal produced from the abovestated discrimination signal generator 631. Following that, the colordifference line sequential signal is subjected to an emphasis process atan emphasis circuit 621. The output of the circuit 621 is supplied to afrequency modulation circuit 622. At the circuit 622, if the input colordifference line sequential signal is frequency modulated as it is,beating would be caused by an aliasing noise. To avoid this, thefrequency modulation is carried out at a high frequency band. Thefrequency modulated signal thus produced from the circuit 622 issupplied via an BPF 623 to a frequency conversion circuit 624 to beconverted to a lower band with a signal of, say, 3.58 MHz which isproduced from a local oscillation circuit 625. The output of the circuit624 is supplied to the other input terminal of the adder 612.

The adder 612 then frequency multiplexes the two input signals thereof.The output of the adder 612 is current amplified by a recordingamplifier 613 and is supplied via a step-up transformer 614 to a mainhead 615.

FIG. 15 shows in a block diagram the reproducing system of the magneticrecording/reproducing apparatus which is the third embodiment of thisinvention. A sub head 701 is arranged to detect a signal which is a highfrequency component having frequencies between 4 and 6 MHz in a videosignal and is recorded within the guard band part of a recording medium.The signal thus detected is taken out from the sub head 701 and issupplied via a step-up transformer 702 to a pre-amplifier 703. Theoutput of the pre-amplifier 703 is supplied to a wave form equalizingcircuit 704 to have the wave form thereof equalized there. The output ofthe circuit 704 is supplied to a frequency demodulation circuit 705 tobe frequency demodulated there. The demodulated signal is then subjectedto a deemphasis process which is carried out by a deemphasis circuit706. The output of the circuit 706 is supplied to a frequency conversioncircuit 707 to be frequency converted upward through a beat-up processcarried out with a signal from a local oscillation circuit 708 as muchas a frequency value decreased by the recording system. The signal whichis thus high frequency band converted is supplied via a BPF 709 to a DCvoltage field offset correction circuit 727. Since the signal has beenoffset as much as Δυ for every horizontal scanning period (l H) by aninterleave process carried out in the recording system, the circuit 727corrects this offset on the basis of a discriminating signal producedfrom an even- or odd-number field discriminating signal generator 741.The output of the circuit 727 is supplied to one of the intput terminalsof an adder 718.

A main head 710 is arranged to detect the video signal (i.e. a frequencycomponent of a frequency band from 0 to 4 MHz) which is recorded on therecording medium. The output signal of the main head 710 is processed bya step-up transformer 711 and a pre-amplifier 712. Following that, thesignal from the main head 710 is divided into a luminance signal and achrominance signal through a BPF 713 and an LPF 720. The luminancesignal from the BPF 713 is processed into a luminance signal offrequencies up to 4 MHz through an ordinary demodulating systemconsisting of a wave form equalizing circuit 714, a frequencydemodulation circuit 715, a deemphasis circuit 716, an LPF 717 and a DCvoltage filed offset correction circuit 728 which is similar to theabove stated circuit 727. The luminance signal thus processed issupplied to the other input terminal of the above stated adder 718. Theadder 718 adds together this signal of frequencies up to 4 MHz and theabove stated high frequency component signal of a frequency band from 4to 6 MHz to obtain thereby the original luminance signal of 6 MHzrecorded on the recording medium.

The chrominance signal from the 720 is supplied to a wave formequalizing circuit 721 to have its wave form equalized there. Thechrominance signal thus processed by the circuit 721 is frequencydemodulated by a frequency demodulation circuit 724 after the frequencyof the signal is raised through a frequency conversion circuit 722 byusing a signal of 3.58 MHz or the like produced from a local oscillationcircuit 723 for the purpose of preventing moire from occurring due toaliasing at the demodulating part. The signal thus demodulated issupplied via an LPF 725 to a color difference concurrence circuit 726 tobe converted into concurrent color difference signals through a suitableinterpolating process carried out on the basis of a signal produced fromthe even- or odd-number field discrimination signal generator 741. Theoriginal luminance signal of 6 MHz is thus obtained together with colordifference signals.

Next, a fourth embodiment of this invention is described as follows: Afeature of the fourth embodiment resides in that: Since the highfrequency component signal has some allowance for the S/N ratio thereof,the crosstalk to the main signal A (having frequencies from 0 to 4 MHz)is lowered by recording the high frequency component signal on arecording medium by lowering the level thereof. The interleaving processis not applied to the main signal but is applied only to the highfrequency component signal which tends to cause a cross-talk.

FIG. 16 shows in a block diagram the recording system of a magneticrecording/reproducing apparatus which is arranged as the fourthembodiment of this invention. In this case, a DC voltage field offsetcircuit 632 for interleaving is provided only in a high frequencycomponent signal processing system for making use of carrier signalshaving interleaving relation with each other as the carrier signals foreffecting the FM modulation. The rest of the arrangement of therecording system of the fourth embodiment is identical with that of thethird embodiment described in the foregoing except that: By adjusting(lowering) the amplification of the recording amplifier 606, the highfrequency component signal is recorded at a lowered level in the guardband part of a recording medium.

FIG. 17 shows in a diagram the reproducing system of the fourthembodiment. Like in the recording system, a DC voltage field offsetcorrection circuit 727 is provided only in a high frequency componentsignal processing system. The rest of arrangement of the reproducingsystem is identical with that of the third embodiment. The fourthembodiment is fundamentally applicable not only to a still video systembut also to any other system that is arranged to have a guard band parton the recording medium.

In the above described embodiment, it is assumed that the video signalis processed by interlace scanning process, and in case where thecarrier signals having interleaving relation with each other are used asthe carrier signals for the FM-modulation the carrier signals arechanged in every field period. However, it is possible to change thecarrier signals in every horizontal scanning period.

If it is assumed, for example, that the video signal is processed bynon-interlace scanning process, it is required to change the carriersignals in every horizontal scanning period in the case where thecarrier signals having interleaving relation are used as the carriersignals for the FM-modulation.

The fourth embodiment of this invention is not only capable of recordinghigh frequency component as described in the foregoing but also hasinterchangeability with a system of the kind handling no high frequencycomponent.

I claim:
 1. An information signal recording apparatus for recording aninformation signal having a predetermined frequency band on a magneticrecording medium, comprising:(a) signal separating means for receivingsaid information signal and for separating the received informationsignal into a first signal having a first frequency band and a secondsignal having a second frequency band which is higher than said firstfrequency band and outputting said first and second signals; (b) firstrecording means having a first magnetic head to record the first signaloutputted from said signal separating means onto a first area of saidmagnetic recording medium by said first magnetic head; and (c) secondrecording means having a second magnetic head, which is different in itsazimuth angle of gap from said first magnetic head, to record the secondsignal outputted from said signal separating means onto a second area ofsaid magnetic recording medium, which is different from said first area.2. An apparatus according to claim 1, wherein said second magnetic headis so arranged that its azimuth angle of gap is 30°-60°.
 3. An apparatusaccording to claim 1, wherein said second recording means is arranged toform a signal recorded track having a width of 24-40 μm, by recordingsaid second signal onto the second area of said magnetic recordingmedium.
 4. An information signal recording apparatus for recording aninformation signal having a predetermined frequency band onto arecording medium, comprising:(a) signal separating means for receivingsaid information signal and for separating the received informationsignal into a first signal having a first frequency band and a secondsignal having a second frequency band which is higher than said firstfrequency band and outputting said first and second signals; (b) firstrecording means for forming a frequency-modulated first signal byfrequency-modulating the first signal outputted from said signalseparating means and for recording said frequency-modulated first signalonto a first area of said recording medium; and (c) second recordingmeans for forming a frequency-modulated second signal, which isinterleaved relatively to said frequency-modulated first signal, byfrequency-modulating the second signal outputted from said signalseparating means and for recording said frequency-modulated secondsignal onto a second area of said recording medium which is differentfrom said first area.
 5. An apparatus according to claim 4, wherein saidrecording medium includes a magnetic recording medium, and said secondrecording means includes a magnetic head having an azimuth angle of gapof 4°-60° and is arranged to record the said frequency-modulated secondsignal onto the second area of said magnetic recording medium by saidmagnetic head.
 6. An apparatus according to claim 4, wherein said secondrecording means has a recording head and is arranged to form a signalrecorded track having a width of 24-40 m, by recording saidfrequency-modulated second signal onto the second area of said recordingmedium.
 7. An information signal recording apparatus for recording afirst information signal having a predetermined frequency band and asecond information signal having a frequency band which is higher thanthe frequency band of said first information signal, onto a magneticrecording medium, comprising:(a) signal separating means for receivingsaid second information signal and for separating the received secondinformation signal into a first signal having a frequency band which issame as that of said first information signal and a second signal havinga frequency band which is higher than that of said first informationsignal and outputting said first and second signals; (b) first recordingmeans having a first magnetic head to record said first informationsignal or said first signal outputted from said signal separating meansonto a first area of said magnetic recording medium by said magnetichead; and (c) second recording means having a second magnetic head,which is different in azimuth angle of gap from said first magnetichead, to record the second signal outputted from said signal separatingmeans onto a second area of said magnetic recording medium, which isdifferent from the first area, by said second magnetic head.
 8. Anapparatus according to claim 7, wherein said magnetic recording mediumincludes a magnetic disc, which is so arranged that concentric firstareas are formed at predetermined distances on said magnetic disc andsecond areas are formed between said first areas.
 9. An apparatusaccording to claim 7, wherein said first information signal includes animage signal and said second information signal includes a highdefinition image signal having a higher resolution than that of saidimage signal.
 10. An information signal recording apparatus forrecording a first information signal having a predetermined frequencyband and a second information signal having a frequency band which ishigher than the frequency band of said first information signal, onto arecording medium, comprising:(a) signal separating means for receivingsaid second information signal and for separating the received secondinformation signal into a first signal having a frequency band which issame as that of said first information signal and a second signal havinga frequency band which is higher than that of said first informationsignal and outputting said first and second signals; (b) first recordingmeans for forming a first frequency-modulated signal byfrequency-modulating said first information signal or said first signaloutputted from said signal separating means and for recording said firstfrequency-modulated signal onto a first area of said recording medium;and (c) second recording means for forming a frequency-modulated secondsignal, which is interleaved relatively to said frequency-modulatedfirst signal, by frequency-modulating the second signal outputted fromsaid signal separating means and for recording said frequency-modulatedsecond signal onto a second area of said recording medium which isdifferent from said first area.
 11. An apparatus according to claim 10,wherein said recording medium includes a magnetic disc.
 12. An apparatusaccording to claim 11, wherein said magnetic disc is so arranged thatconcentric first areas are formed at predetermined distances on saidmagnetic disc and second areas are formed between said first areas. 13.An apparatus according to claim 11, wherein said first recording meansincludes a first magnetic head and is arranged to record said firstfrequency-modulated signal onto a first area of said magnetic disc bysaid first magnetic head, and said second recording means includes asecond magnetic head, which is different in azimuth angle of gap fromsaid first magnetic head and is arranged to record said secondfrequency-modulated signal onto a second area of said magnetic disc bysaid second magnetic head.
 14. An apparatus according to claim 10,wherein said first information signal includes an image signal and saidsecond information signal includes a high definition image signal havinga higher resolution than that of said image signal.